1. Field of the Invention
The present invention relates to a method of manufacturing a nitride system III-V compound layer including a group III element and nitrogen (N) as a group V element and a method of manufacturing a substrate employing the method of manufacturing a nitride system III-V compound layer.
2. Description of the Related Art
In recent years, demand for high density or high resolution recording/reproducing in optical disks and magnetic optical disks has grown. To fulfill this demand, research on semiconductor devices capable of emitting lights in a short-wavelength range within an ultraviolet spectrum or a green-wavelength spectrum has been actively conducted. As suitable materials constituting such a semiconductor device capable of emitting lights in the short-wavelength range, nitride system III-V compound semiconductors such as GaN, AlGaN mixed crystal or GaInN mixed crystal are known (Jpn. J. Appl. Phys., 30 (1991), L1998).
Generally, light-emitting devices using the nitride system III-V compound semiconductor are manufactured by sequentially growing layers made of the nitride system III-V compound semiconductor on a substrate using a metal organic chemical vapor deposition (MOCVD) method or a using a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method. As the substrate, a sapphire (Al2O3) substrate or a silicon carbide (SiC) substrate is used in general.
However, a lattice constant and a thermal expansion coefficient of sapphire and silicon carbide and those of the nitride system III-V compound semiconductor are different, so that there is a problem such that defects or cracks occur in a grown nitride system III-V compound semiconductor layer. Further, when manufacturing a semiconductor laser diode (LD) as a semiconductor light-emitting device, it is difficult to perform cleavage in order to form end faces of a resonator.
These problems are considered to be solved by the use of a substrate made of nitride system III-V compounds. In a case where the nitride system III-V compound semiconductor layer is grown on the substrate made of the nitride system III-V compound, occurrence of defects or cracks is suppressed because their lattice constants and thermal expansion coefficients are almost identical. Further, when manufacturing a semiconductor laser, for formation of end faces of a resonator, cleavage is easily performed. Accordingly, it is considered that a highly reliable semiconductor light-emitting device is manufactured with excellent yield.
The nitride system III-V compound has a high saturated vapor pressure. Thus, a manufacturing method which is generally used when manufacturing a substrate made of silicon (Si) or a substrate made of gallium arsenide (GaAs) cannot be used for manufacture of the substrate made of the nitride system III-V compound. Heretofore a well-known method for manufacturing the substrate made of the nitride system III-V compound is a method such that the nitride system III-V compound is grown on a growth base made of sapphire or gallium arsenide to achieve a predetermined thickness using a MOCVD method, MBE method or hydride vapor phase epitaxy (HVPE) method in which hydride is used as a source material. With the use of the HVPE method among these method, the nitride system III-V compound can be grown for several xcexcm to several hundreds xcexcm per one hour, thus the nitride system III-V compound can be grown to achieve a usable thickness as a substrate for a short period of time. As such a nitride system III-V compound substrate manufactured using the HVPE method, a nitride system III-V compound substrate manufactured by growing GaN on the aforementioned growth base has been reported.
Further, a method such that a buffer layer such as a low temperature buffer layer is provided on a growth base and a nitride system III-V compound is grown on the buffer layer, thereby manufacturing the nitride system III-V compound substrate is known.
However, with the method of growing the nitride system III-V compound substrate directly on the growth base, the condition of the surface after growth is bad, and further the quality is not sufficient for the use as a substrate for growing a good-quality nitride system III-V compound semiconductor.
Moreover, with the method for growing the nitride system III-V compound on a growth base having the buffer layer in between, an extra step for providing the buffer layer is necessary, which lowers productivity. Specifically, when a low temperature buffer layer is provided as the buffer layer, after performing cleaning or the like on the growth base in the high temperature environment, a temperature has to be lowered once, which further lowers the productivity.
The present invention has been achieved in view of the above problems. It is an object of the invention to provide a method of manufacturing a nitride system III-V compound layer which improves the quality and facilitates the manufacturing process and a method of manufacturing a substrate employing the method of manufacturing a nitride system III-V compound layer.
According to the present invention, a method of manufacturing a nitride system III-V compound layer including at least one selected from a group consisting of gallium (Ga), aluminum (Al), boron (B) and indium (In) as a group III element and at least nitrogen (N) as a group V element comprises a first growth step for growing a first growth layer including a nitride system III-V compound at a first growth rate, and a second growth step for growing a second growth layer including a nitride system III-V compound at a second growth rate lower than the first growth rate.
According to the invention, a method of manufacturing a substrate made of a nitride system III-V compound including at least one selected from a group consisting of gallium (Ga), aluminum (Al), boron (B) and indium (In) as a group III element and at least nitrogen (N) as a group V element comprises a first growth step for growing a first growth layer including the nitride system III-V compound at a first growth rate, and a second growth step for growing a second growth layer including the nitride system III-V compound at a second growth rate lower than the first growth rate.
With the method of manufacturing a nitride system III-V compound layer of the invention and the method of manufacturing a substrate of the invention, the first growth layer is grown at the first growth rate and the second growth layer is grown at the second growth rate lower than the first growth layer.
Other and further objects, features and advantages of the invention will appear more fully from the following description.